The goal of this proposal is to understand the neural mechanisms of social recognition and memory. This information will lead to a more thorough understanding of the brain, and especially of higher-order sensory processes associated with the olfactory and vomeronasal senses. In addition, the research will provide a new, unique perspective on the functional neuroanatomy of memory by investigating the role of various brain loci in social memory. Understanding of the brain, and especially of social recognition and memory processes, is relevant to the understanding of many types of human disabilities due to stroke or head injury, and also to understanding the deficits caused by a variety of degenerative diseases, including Alzheimer's disease and Korsakoff's syndrome. The specific aims of the study are to use the extensive knowledge obtained about social communication in hamsters as a model system to investigate the neural mechanisms of individual recognition by odors. Three approaches will be employed. First the roles of three different brain systems in individual recognition and memory will be studied by use of lesions. The effects of stereotaxic lesions, placed in (1) thalamus and neocortex, (2) entorhinal cortex and hippocampus, or (3) various parts of the amygdala, will be evaluated using a battery of behavioral tests. Second, cells that are activated during individual discrimination will be studied by histological methods, initially with a stains for the immediate early gene c-fos. Third, the roles of the vomeronasal and olfactory sensory systems will be investigated using lesions of the peripheral receptors. The abilities of animals to discriminate and recognize individuals after such lesions will be evaluated, thus demonstrating the roles of these two sensory systems in providing the initial input of individually distinctive information. These converging lines of evidence should provide a basis for further, finer-grained anatomical and neurophysiological investigations of social recognition and should provide a compelling addition to other approaches to the neural basis of learning and memory.